The present invention relates to a circuit for noise suppression in measuring signals.
The German Patent GermanPatent No. 2,118,812 describes a device for forming the mean value of signals representing statistically occurring events. This known device is contructed as follows: The measuring signal is fed to a differentiating circuit which controls a signal monitoring circuit. This monitoring circuit determines whether a change in the input signal (time derivative) is zero or not zero. The monitoring circuit has a two channel output respectively connected to two function generators, and one or the other is actuated depending on the outcome of the zero/non-zero test.
One of the function generators, generall, produces a function x = f (t) and the other one the function x = f x = f (dU .sub.i /dt ), wherein U.sub.i is the input signal. The values for x (in either case) are used to control an integrator via a differential amplifier, but not as input to be integrated. The integrator has a time constant .tau. which is controlled in dependence upon x, so that for x = f (dU.sub.i /dt ) the value of .tau. is reduced, and for x = f (t) the value for x is increased. The input proper for the integrator is U.sub.i itself and the integrator furnishes a signal U.sub.o = .intg. U.sub.i. The differentiator, the monitor and the function generators are connected in a feedback loop of the device via the differential amplifier.
The above-mentioned patent discloses also a second embodiment in which the differentiating circuit is replaced by a second differential amplifier, forming the difference between the signals U.sub.i and U.sub. o .
The known device, in either configuration, works in that for large changes in the input signal U.sub.i the integrator operates automatically with a small time constant, but with a large time constant for small input changes. In either case, the device operates with a finite time constant. It was found that this feature amounts to a drawback in that for a sudden change in the input (step function) the output changes rather slowly by an e-function so that the indicated value deviates from the true value for the input.